1. Field of the Invention
The present invention relates to a process for encoding digitized images to reduce storage requirements to completely store the digitized image. A digitized image is formed by sampling a plurality of points in an analog image and storing the value of each point as a binary one or a zero.
2. Description of the Prior Art
The assignee of the present invention has marketed a high speed printer under the trademarks ANSER I and VISION which prints documents such as, but not limited to, business forms from stored digitized images. These printers have a print engine manufactured under one or more of U.S. Pat. Nos. 4,155,093, 4,160,257, 4,267,556, 4,365,549 and 4,379,969. The print engine has a dot matrix array in which individual points are selectively printed with a dark dot by the simultaneous application of a high frequency potential between a selector bar and ground and a direct current potential between a finger electrode and a dielectric receptor counterelectrode as described in U.S. Pat. No. 4,155,093. A drum is charged with the image which is toned and transferred to the sheet to be printed. The toner is cold fused.
The aforementioned ANSER I and VISION systems drive the dot matrix from a digitized image which is stored in memory without data compaction of the number of individual points of the digitized image by an encoding technique.
The assignee experimented with a form of run length encoding for compressing a digitized image of typical business forms in the VISION system. While this process produced an acceptable degree of data compression in the storage of the digitized image, the process was complicated to implement in hardware because of the necessity of rotation and shifting cycles to process the individual bits. High speed processing of digital images is required for high speed printers such as the ANSER I and VISION systems to achieve high printing throughputs. For printing a repertoire of forms which each have recurring information of a fixed format, a technique is needed to reduce the memory requirements for storage of the fixed format component to permit multiple formats to be stored efficiently in memory of the printing systems which may be read out without taking too many bus cycles and requiring continued access to the working memory for read out which interferes with the controller's access to the memory to execute other functions.
The high resolution of the print engine in the VISION of 240 pixels per inch necessitates the use of considerable memory to store even the simplest of forms. The storing of a number of digitized forms each as a full bit map which could be selectively called would consume a considerable amount of the working space in a disk unit of the VISION control system possibly preventing the storage of other information and interfering with communications of the disk unit with other parts of the system. Moreover, transmitting large amounts of data from a disk unit to the print engine can be time consuming which would influence throughput.
The known data compaction technique of run length encoding encodes a string of identical bits by the coding of the length of the string of identical bits. Run length encoding can achieve high degrees of compaction. Run length encoders may process the bits in serial or parallel form.
U.S. Pat. No. 4,327,379 discloses an encoding technique for a digitized image which encodes the number of all multibit nibbles storing all zeros in a field followed by the actual bits of a terminating nibble having at least one bit storing a one value. This technique does not encode the number of nibbles having only the level of last bit of the nibble storing at least one bit having a one level which sequentially follow the nibble storing at least one bit as one.